[media] dvb_frontend: add props argument to dtv_get_frontend()

Instead of implicitly using the DTV cache properties at
dtv_get_frontend(), pass it as an additional argument.

This patch prepares to use a separate cache for G_PROPERTY,
in order to avoid it to mangle with the DVB thread
zigzag logic.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>